[ASME 2016 24th International Conference on Nuclear Engineering - Charlotte, North Carolina, USA (Sunday 26 June 2016)] Volume 4: Computational Fluid Dynamics (CFD) and Coupled Codes; Decontamination and Decommissioning, Radiation Protection, Shielding, and Waste Management; Workforce Development, Nuclear Education and Public Acceptance; Mitigation Strategies for Beyond Design Basis Events; Risk Management - Overview of Code Structures, Challenges and Available Methodologies for Treatment of Model Uncertainty in Severe Accident Calculations